1. Field of the Invention
The present invention relates to a battery assembly system used for an electric vehicle. In particular, the present invention relates to a battery assembly system capable of suppressing flow of electrolyte out of an exhaust passage when an abnormality occurs in cells composing the battery assembly and the electrolyte is released in a mist state from the cells.
2. Description of the Prior Art
In general, a battery assembly with a plurality of cells connected in series or in parallel is mounted in an electric vehicle such as an electric car, etc., in order to supply a motor etc. with power for driving a vehicle. In this case, due to the variation of the battery characteristic, electric currents are concentrated on a specific cell, or overcharge or overdischarge of the cell easily occurs. When such overcharge or overdischarge of the cell, or internal shorts in the cell occur, a safety valve or a battery case may be damaged. As a result, an electrolyte may be released in a mist state from the damaged portion.
A battery used for this kind of application can be used over a longer term, if the working temperature is always in the predetermined range. Therefore, in order to secure and extend a lifetime of battery, a branching is provided at a middle portion of a duct for introducing air into a cabin from the outside the car, and a duct for introducing air into a case for housing a battery assembly is connected to this branching portion. Furthermore, an exhaust duct for exhausting the introduced air is connected to the case for housing the battery assembly.
The air flowing in the exhaust duct is allowed to return to a cabin. JP10 (1998)-252467A suggests a technique in which, when the abnormality occurs in the cells, gas is prevented from flowing into the cabin by providing a switching damper for releasing the air flowing in the exhaust duct to the outside of the cabin. Furthermore, JP7 (1995)-245089A discloses a mechanism in which a tube is provided for a safety valve of a cell, thereby capturing mists without using a switching damper.
However, when the abnormality occurs in the cell, if employing the configuration having the switching damper for releasing the air flowing in the exhaust duct to the outside of the cabin, the system is somewhat complicated. Furthermore, if air is always allowed to exhaust to the outside of the car, the efficiency of heating and cooling in the cabin is deteriorated.
On the other hand, with the mechanism in which a tube is provided for the safety valve of the cell so as to capture the mist, the cost is increased in the apparatus. Furthermore, when a battery case is made of a resin, the strength of the battery case is lower than the strength of a metal battery case. Therefore, when the battery case is damaged due to overcharge or overdischarge of a cell or internal short in the cell, the mist-state electrolyte may flow into the exhaust duct.
It is an object of the present invention to solve the conventional problems described above by providing a simple and inexpensive battery assembly system used for an electric vehicle, which can suppress the flow of electrolyte out of an exhaust passage even if the electrolyte is released in a mist state from the cell.
In order to achieve the above-mentioned object, a configuration of a battery assembly system used for an electric vehicle of the present invention includes a battery assembly with a plurality of cells electrically connected, a battery assembly case for housing the battery assembly with the battery assembly mechanically held, a fan for drawing air into the inside of the battery assembly case, and an exhaust passage for allowing air to be exhausted from the battery assembly case, wherein the exhaust passage is provided with a mechanism for capturing an electrolyte released in a mist state from the cell. According to such a configuration of the battery assembly system used for an electric vehicle, it is possible to suppress the flow of electrolyte released from a damaged portion of the safety valve or the battery case of the cells out of the exhaust passage.
Furthermore, in the configuration of the battery assembly system used for the electric vehicle of the present invention, it is preferable that a fan is provided in the exhaust passage and the electrolyte is captured by the fan. According to such a preferable configuration, it is possible to prevent a mist-state electrolyte from flowing out of the exhaust passage by the use of existing components of the battery assembly system. Furthermore, in this case, it is preferable that the fan is a sirocco fan or an axial-flow fan. According to such a preferable configuration, it is possible to capture the mist-state electrolyte effectively since a part of the mist-state electrolyte collides with and is attached to the cascade of the fan and a part of the rest of the mist-state electrolyte collides with and is attached to the wall surface of the fan by the inertial force.
Furthermore, in the configuration of the battery assembly system used for the electric vehicle of the present invention, it is preferable that a filter further is provided in the exhaust passage and the electrolyte is captured by the filter. According to such a preferable configuration, the electrolyte released in a mist state from the damaged portion of the safety valve or battery case of the cell collides with and is attached to the filter. In other words, the mist-state electrolyte released from the cell is captured in the exhaust passage. Thus, it is possible to suppress the release of mist-state electrolyte out of the exhaust passage. Furthermore, in this case, it is preferable that the filter can capture the electrolyte released in a mist state having a particle size of 1 xcexcm to 50 xcexcm. According to such a preferable configuration, it is possible to capture the mist-state electrolyte having a small diameter and higher scattering property. The mist has a nature in that as the particle diameter of the mist is smaller, the scattering property of the mist is increased. Therefore, unless the filter can capture the mist having particles at least as small as the particle size mentioned above, i.e. particle size of 1 xcexcm to 50 xcexcm, the filter is not as useful for practical purposes.
Furthermore, in the configuration of the battery assembly system used for the electric vehicle of the present invention, it is preferable that the exhaust passage is an exhaust duct.
Furthermore, in the configuration of the battery assembly system used for the electric vehicle of the present invention, it is preferable that the exhaust passage is an exhaust duct and the exhaust duct has a bend portion for capturing the electrolyte. According to such a preferable configuration, a part of the mist-state electrolyte collides with and is attached to the wall surface of the bend portion by the inertial force and a part of the rest of the mist-state electrolyte collides with and is attached to the wall surface of the exhaust duct by the air that is made turbulent by the bend portion. Thus, the mist-state electrolyte released from the cell is captured in the exhaust duct and its flow out of the exhaust duct is suppressed. Furthermore, in this case, it is preferable that the bend portion is provided with an angle of 60xc2x0 to 160xc2x0. According to such a preferable configuration, it is possible to capture efficiently the mist-state electrolyte released from the cell in the exhaust duct.
Furthermore, in the configuration of the battery assembly system used for the electric vehicle of the present invention, it is preferable that the exhaust passage is an exhaust duct and the exhaust duct is provided with convex and concave portion on the inner wall for capturing the electrolyte. According to such a preferable configuration, the mist-state electrolyte is attached to the convex and concave portion on the inner wall and captured in the exhaust duct.
Furthermore, if at least two of the configurations of the present invention are provided, it is possible to capture the mist state electrolyte released from the cell in the exhaust passage reliably.
Furthermore, in the configuration of the battery assembly system used for the electric vehicle of the present invention, it is preferable that the electrolyte released a mist state from the cell is an alkaline electrolyte including potassium hydroxide as a main component, and the aerial concentration of the potassium hydroxide in the air of the cabin of the electric vehicle is 2 mg/m3 or less. Furthermore, it is preferable that the aerial concentration of the potassium hydroxide is 0.3 mg/m3 or less.